Wire carriers typically comprise a continuous wire weft formed into a zig-zag formation with substantially parallel limbs interconnected by connecting regions at each end of the limbs onto which weft is knitted, sewn, threaded, or otherwise disposed a plurality of warp threads. These warp threads are typically a synthetic resin or a natural fiber.
Such a wire carrier is widely used, mainly as a reinforcing frame for coated polymeric products, especially extrusion coated products, such as weather seals on motor vehicles. During manufacture of the seals, the carrier is passed through an extruder and is thus subjected to stresses and temperatures which can cause the warp threads to drift laterally, stretch longitudinally and degenerate both physically and chemically. This can result, for example, in breakage of the warps and distortion of the wire carrier which affects the extrusion process and leads to reduced quality and performance of the corresponding seal. In forming and extrusion processes drifting of the warp threads can cause air bubbles and exposure of the wire in the final weather seal. Finally, when the warp threads are thus processed with a tensile stress during extrusion, the resultant product may experience shrinkage after being final sized and installed, which becomes a problem for the end customer. There has long been a need to develop a stable wire carrier for extruded and molded polymeric products which overcomes these problems and some attempts have been made without complete success.
The prior art has shown attempts at solving some of the above-described problems. One attempt to solve the problem of lateral warp shifting formed adjacent zig-zag loops into a propeller or banana shape, but this is difficult to control, and has little effect on preventing lateral warp drifting.
In another attempt to solve the problem of warp drift, Beck et al, EP Application No. 0175818, have suggested a knitted wire carrier with knotted junctions between the warp threads and the wire weft. Both the warp threads and the wire weft comprise polymeric or polymeric coated material and the polymeric material of the warp and the weft must both be melted to form a weld or fusion at the crossover points. This structure suffers from several disadvantages. It is difficult and expensive to provide either a polymer-coated wire weft, or the combination of an uncoated wire weft with a polymeric material which is fed to the knitting machine with the wire. Furthermore, the use of polymeric meltable materials in both the warp and weft increases the cost of the wire carrier. These disadvantages increase the costs enough that it could not be used commercially.
EP 0384613 discloses a knitted wire carrier in which stitched warp threads comprise two threads of polymeric material having different melting points such that when the melting point of the lower melting thread is exceeded the melted thread causes the other thread to be attached to the wire weft. This structure allows single strands of warp thread plied with a meltable filament to be bonded to the wire carrier wherever they are knitted.
Similarly, U.S. Pat. No. 5,416,961 to Vinay discloses a knitted wire carrier comprising at least one meltable filament laid-in into at least two adjacent warp threads, whereby on heating, the melted filament causes the at least two adjacent warp threads to be bonded to the wire and/or to each other for stabilizing the resulting wire carrier against warp drift. While the above constructions address warp drift, they do not address elongation.
The use of various materials for warp threads also does not solve the problem of elongation. That is, even using warp threads made from materials having zero to very low elongation factors does not completely prevent a wire carrier from suffering from elongation and eventual shrinkage. For example, even if fiberglass threads, which have a very low elongation factor, were used as the warp threads in a wire carrier, the knotted junctions of the threads wrapped around the carrier takes away from the ability of the threads to completely prevent elongation. While the short pieces of thread between the knots may be free of elongation during extrusion, the knots themselves are apt to become tighter during extrusion and looser after processing. Thus, tying knots in fiberglass or other threads with very low elongation factors takes away their ability to effectively prevent elongation throughout the wire carrier.
Thus, none of the above described constructions provides an entirely satisfactory structure for a wire carrier having warp threads attached to a wire support for use in a weather seal because none address the issue of shrinkage in the final product resulting from elongation of the warp threads during extrusion.
Thus, there is a need to reduce final product shrinkage by reducing wire carrier elongation during preforming, extrusion, and postforming. There is further a need to reduce the shrink that is realized in weather seals in the short term after extruding, during secondary operations, and after extended time in the field. There is further a need to retain the spacing between generally parallel limbs of a wire weft during extrusion processing for prevention of elongation. There is further a need for a simple, inexpensive elongation prevention mechanism to solve the above needs. There is further a need for such an elongation prevention mechanism which is easy to incorporate into the manufacture of a wire carrier.